Quantitative assessment of structural inhomogeneity in cold-resistant low-alloy steel sheets for interpretation of technological features of their manufacturing

2020 ◽  
pp. 4-14
Author(s):  
A. A. Kazakov ◽  
◽  
D. V. Kiselev ◽  
O. V. Sych ◽  
E. I. Khlusova ◽  
...  
Keyword(s):  
Quantitative Assessment ◽  
Complex Analysis ◽  
Volume Fraction ◽  
Thermomechanical Processing ◽  
Granular Bainite ◽  
Accelerated Cooling ◽  
Subgrain Structure ◽  
Long Distance ◽  
Lath Bainite ◽  
Detailed Interpretation

Microstructural inhomogeneity comparative automated complex analysis of plate low-alloy cold-resistant steels for Arctic application with a thickness of 25, 50 and 70 mm, produced by thermomechanical processing technology with various temperaturedeformation parameters, has been performed. The inhomogeneity of the microstructure over the plates thickness was estimated by the volume fraction of coarse packet-block regions of lath bainite and regions of bainite that does not have a developed internal subgrain structure (conventionally called “non-granular” bainite), as well as anisotropy of the microstructure at different dimensional levels: short and long distance neighborhoods. The obtained results of microstructural heterogeneity quantitative assessment over the plates thickness were used for its detailed interpretation, taking into account the metallurgical inheritance of the slab and special features of two-stage thermomechanical processing with accelerated cooling.

scholarly journals Quantitative assessment of microstructural inhomogeneity by thickness of hot-rolled plates made of cold-resistant low-alloy steel for Arctic applications

2020 ◽  
pp. 41-49
Author(s):  
A. A. Kazakov ◽  
D. V. Kiselev ◽  
O. V. Sych ◽  
E. I. Khlusova
Keyword(s):  
Volume Fraction ◽  
Thermomechanical Processing ◽  
Rolling Direction ◽  
Accelerated Cooling ◽  
Subgrain Structure ◽  
Plate Steel ◽  
Long Distance ◽  
Microstructural Heterogeneity ◽  
Hot Rolled ◽  
Rolled Plates

A technique to assess microstructural anisotropy assessing by the thickness of the plate steel based on the texture analysis of the image has been developed. This technique provides for the anisotropy assessment at two dimensional levels: in the short-distance and long-distance neighborhoods, which characterize the elongation along the rolling direction of fine and coarse structural constituents, respectively. The practical approval results of this technique in the study of the microstructural heterogeneity of ferritic-bainitic steels over the thickness of 25–70 mm hot-rolled plates have been presented. It has been shown that the proposed anisotropy criteria in combination with the volume fraction of coarse packet-block regions of lath bainite as well as regions of bainite without an internal developed subgrain structure adequately estimate the microstructural heterogeneity over the thickness of plate steel and can be used for a detailed interpretation of the two-stage thermomechanical processing technology with accelerated cooling including taking into account the metallurgical inheritance of the slab.

Scientific and technological bases for creation of cold-resistant steel with a guaranteed yield strength of 315–750 MPa for the Arctic. Part 2. Technology of production, structure and properties of sheet hire performance

2019 ◽  
pp. 14-41
Author(s):  
O. V. Sych
Keyword(s):  
Yield Strength ◽  
Thermomechanical Processing ◽  
The Arctic ◽  
Accelerated Cooling ◽  
Low Alloy Steels ◽  
Hot Plastic Deformation ◽  
Metal Thickness ◽  
Alloy Steels ◽  
Technology Of Production ◽  
Technological Methods

On the basis of the conducted research, a complex of scientific and technological methods has been developed for various technological processes (thermomechanical processing with accelerated cooling, quenching from rolling and separate furnace heating with high-temperature tempering). The developed method provides the formation of the structure of acceptable heterogeneity and anisotropy according to different morphological and crystallographic parameters throughout the thickness of rolled products up to 100 mm from low alloy steels with a yield strength of at least 315–460 MPa and up to 60 mm from economically alloyed steels with a yield strength of at least 500–750 MPa. The paper presents results of the industrial implementation of hot plastic deformation and heat treatment schemes for the production of cold rolled steel sheet with yield strength of at least 315–750 MPa for the Arctic. The structure of sheet metal thickness is given, providing guaranteed characteristics of strength, ductility, cold resistance, weldability and crack resistance.

Modeling of steel hardening process at thermal and mechanical treatment

2019 ◽  
pp. 7-13
Author(s):  
A. S. Oryshchenko ◽  
V. A. Malyshevsky ◽  
E. A. Shumilov
Keyword(s):  
Mechanical Treatment ◽  
Thermomechanical Processing ◽  
High Strength Steels ◽  
High Strength ◽  
Accelerated Cooling ◽  
Rolling Mills ◽  
Hardening Process ◽  
Deformation Parameters ◽  
Research Complex ◽  
Steel Hardening

The article deals with modeling of thermomechanical processing of high-strength steels at the Gleeble 3800 research complex, simulating thermomechanical processing with various temperature and deformation parameters of rolling and with accelerated cooling to a predetermined temperature. The identity of steel hardening processes at the Gleeble 3800 complex and specialized rolling mills, as well as the possibility of obtaining steels of unified chemical composition, are shown.

scholarly journals Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 939 ◽  
Author(s):  
Yun Zong ◽  
Chun-Ming Liu
Keyword(s):  
Impact Toughness ◽  
Cooling Rate ◽  
Vickers Hardness ◽  
Heat Affected Zone ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Low Carbon ◽  
Transformation Diagram ◽  
Lath Bainite ◽  
Continuous Cooling Transformation Diagram

In order to provide important guidance for controlling and obtaining the optimal microstructures and mechanical properties of a welded joint, the continuous cooling transformation diagram of a new low-carbon Nb-microalloyed bainite E550 steel in a simulated coarse-grain heat-affected zone (CGHAZ) has been constructed by thermal dilatation method in this paper. The welding thermal simulation experiments were conducted on a Gleeble-3800 thermo-mechanical simulator. The corresponding microstructure was observed by a LEICA DM2700M. The Vickers hardness (HV) and the impact toughness at −40 °C were measured according to the ASTM E384 standard and the ASTM E2298 standard, respectively. The experimental results may indicate that the intermediate temperature phase transformation of the whole bainite can occur in a wide range of cooling rates of 2–20 °C/s. In the scope of cooling rates 2–20 °C/s, the microstructure of the heat-affected zone (HAZ) mainly consists of lath bainite and granular bainite. Moreover, the proportion of lath bainite increased and granular bainite decreased as the cooling rate increasing. There is a spot of lath martensite in the microstructure of HAZ when the cooling rate is above 20 °C/s. The Vickers hardness increases gradually with the increasing of the cooling rate, and the maximum hardness is 323 HV10. When the cooling time from 800 °C to 500 °C (t8/5) is 5–15 s, it presents excellent −40 °C impact toughness (273–286 J) of the CGHAZ beyond the base material (163 J).

scholarly journals Welding thermal cycle-triggered precipitation processes in steel S700MC subjected to the thermo-mechanical control processing

2017 ◽  
Vol 62 (1) ◽  
pp. 321-326 ◽  
Author(s):  
J. Górka
Keyword(s):  
Thermomechanical Processing ◽  
Control Process ◽  
Base Material ◽  
Structural Defects ◽  
Accelerated Cooling ◽  
Internal Stresses ◽  
Mechanical Control ◽  
Thin Foils ◽  
Precipitation Processes ◽  
The Matrix

Abstract This study presents tests concerned with welding thermal process-induced precipitation processes taking place in 10 mm thick steel S700MC subjected to the Thermo-Mechanical Control Process (TMCP) with accelerated cooling. The thermomechanical processing of steel S700MC leads to its refinement, structural defects and solutioning with hardening constituents. Tests of thin foils performed using a transmission electron microscope revealed that the hardening of steel S700MC was primarily caused by dispersive (Ti,Nb)(C,N) precipitates (being between several and less than twenty nanometers in size). In arc welding, depending on a welding method and linear energy, an increase in the base material in the weld is accompanied by the increased concentration of hardening microagents in the weld. The longer the time when the base material remains in the liquid state, the greater the amount of microagents dissolved in the matrix. During cooling, such microagents can precipitate again or remain in the solution. An increase in welding linear energy is accompanied by an increase in the content of hardening phases dissolved in the matrix and, during cooling, by their another uncontrolled precipitation in the form of numerous fine-dispersive (Ti,Nb)(C,N) precipitates of several nm in size, leading to a dislocation density increase triggered by type 2 internal stresses.

Development of X80M Line Pipe Steel for Spiral Welded Pipes With Low Temperature Toughness and Excellent Weldability

2014 ◽  
Author(s):  
Nuria Sanchez ◽  
Özlem E. Güngör ◽  
Martin Liebeherr ◽  
Nenad Ilić
Keyword(s):  
Low Temperature ◽  
Life Cycle Cost ◽  
Volume Fraction ◽  
Large Diameter ◽  
Pipe Production ◽  
Strain Accumulation ◽  
Long Distance ◽  
Line Pipe ◽  
Low Temperature Toughness ◽  
Welded Pipe

The unique combination of high strength and low temperature toughness on heavy wall thickness coils allows higher operating pressures in large diameter spiral welded pipes and could represent a 10% reduction in life cycle cost on long distance gas pipe lines. One of the current processing routes for these high thickness grades is the thermo-mechanical controlled processing (TMCP) route, which critically depends on the austenite conditioning during hot forming at specific temperature in relation to the aimed metallurgical mechanisms (recrystallization, strain accumulation, phase transformation). Detailed mechanical and microstructural characterization on selected coils and pipes corresponding to the X80M grade in 24 mm thickness reveals that effective grain size and distribution together with the through thickness gradient are key parameters to control in order to ensure the adequate toughness of the material. Studies on the softening behavior revealed that the grain coarsening in the mid-thickness is related to a decrease of strain accumulation during hot rolling. It was also observed a toughness detrimental effect with the increment of the volume fraction of M/A (martensite/retained austenite) in the middle thickness of the coils, related to the cooling practice. Finally, submerged arc weldability for spiral welded pipe manufacturing was evaluated on coil skelp in 24 mm thickness. The investigations revealed the suitability of the material for spiral welded pipe production, preserving the tensile properties and maintaining acceptable toughness values in the heat-affected zone. The present study revealed that the adequate chemical alloying selection and processing control provide enhanced low temperature toughness on pipes with excellent weldability formed from hot rolled coils X80 grade in 24 mm thickness produced at ArcelorMittal Bremen.

Influence of Omega-Phase Precipitation Hardening on the Static and Dynamic Properties of Metastable Beta Ti-Nb-Zr and Ti-Nb-Ta Alloys

2013 ◽  
Vol 738-739 ◽  
pp. 189-194 ◽  
Author(s):  
Vladimir Brailovski ◽  
Sergey Prokoshkin ◽  
Karine Inaekyan ◽  
Sergey Dubinskiy
Keyword(s):  
Mechanical Behavior ◽  
Volume Fraction ◽  
Thermomechanical Processing ◽  
Subgrain Size ◽  
Dynamic Properties ◽  
Aging Treatment ◽  
Stress Generation ◽  
Phase Precipitation ◽  
Superelastic Behavior ◽  
Temperature Scanning

The influence of thermomechanical processing on the Ti-21.8Nb-6Zr (TNZ) and Ti-19.7Nb-5.8Ta (TNT) (at%) alloys’ structure, phase composition, mechanical and functional properties is studied. Both alloys possess polygonized dislocation substructure (average subgrain size  100 nm), and manifest superelastic behavior at room temperature and recovery stress generation during constant-strain temperature scanning experiments. After aging treatment, both alloys were -phase precipitation hardened, but their mechanical behavior was impacted differently -- it was detrimental for TNZ and beneficial for TNT. The different impact of aging heat treatment on the mechanical behavior of these alloys is explained by the differences in the -phase nucleation rate, precipitates’ size, shape, volume fraction and distribution, and by their effect on the alloys’ critical stresses and transformation temperatures.

scholarly journals Experimental Research on Fatigue Properties of X80 Pipeline Steel for Synthetic Natural Gas Transmission

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Li Yan–hua ◽  
Feng Hui ◽  
Chi Qiang ◽  
Fei Fan ◽  
Gao Xiong-xiong ◽  
...  
Keyword(s):  
Natural Gas ◽  
Base Metal ◽  
Hydrogen Content ◽  
Volume Fraction ◽  
Pipeline Steel ◽  
Fatigue Properties ◽  
High Grade ◽  
Long Distance ◽  
X80 Pipeline Steel ◽  
Synthetic Natural Gas

In recent years, many synthetic natural gas demonstration projects have been put into operation all over the world, and hydrogen is usually contained in synthetic natural gas. X80 is the most commonly used high-grade pipeline steel in the construction of natural gas pipelines. The compatibility between high-grade pipeline steel and hydrogen directly affects safety and reliability of long-distance pipelines. Therefore, in order to study the effect of hydrogen content on fatigue properties of high-grade pipeline steel, fatigue specimens were taken from base metal, spiral welds, and girth weld of submerged arc spiral welded pipes, respectively. Specifically, the total pressure was 12 MPa and hydrogen content was from 0 to 5vol%. Experimental results indicate that the hydrogen significantly increases the fatigue crack growth rate for both base metal, spiral weld, and heat-affected zone of X80 pipeline steel for about ten times compared with reference environment nitrogen, hydrogen would greatly reduce the fatigue life of the X80 pipeline steel, and the fatigue lifetime would decrease with the increase in hydrogen volume fraction. In order to ensure the safe operation of SNG pipeline, the hydrogen content should be controlled as low as possible.

scholarly journals Morphological and Crystallographic Characteristics of α Structure in a Low-Carbon Iron–Nickel Alloy

Crystals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 468 ◽  
Author(s):  
Gaojun Mao ◽  
Cyril Cayron ◽  
Xiuli Mao ◽  
Rui Cao ◽  
Roland Logé ◽  
...  
Keyword(s):  
Lath Martensite ◽  
Granular Bainite ◽  
Body Centered Cubic ◽  
Low Carbon ◽  
Electron Backscattered Diffraction ◽  
Dislocation Densities ◽  
Lath Bainite ◽  
Crystallographic Characteristics ◽  
Iron Nickel ◽  
Relationship Of

The features of α (body-centered cubic) structures were investigated in a low-carbon multicomponent alloy from morphological and crystallographic perspectives. In addition to apparent features of granular bainite and lamellar martensite, a morphological similarity can be found between lath martensite and lath bainite. Therefore, it is of interest to explore possible discrepancies between lath martensite and lath bainite from a crystallographic perspective. These microstructures were obtained by various cooling rates (i.e., water quenching, 5 °C/s, and 0.05 °C/s) and then were characterized by a combination of scanning electron microscopy and electron backscattered diffraction techniques. It is shown that: (1) Lath martensite (LM) formed in the samples that were water-quenched, and a mixture of LM and lath bainite (LB) and granular bainite (GB) formed in the samples cooled at rates of 5 °C/s and 0.05 °C/s, respectively; (2) A Kurdjumov-Sachs relationship was mostly found in as-quenched martensite, while a Greninger-Troiano relationship represented the orientation relationship of LB and GB; (3) As the cooling rate decreased, the dislocation densities in corresponding microstructures were reduced, while the tendency of variant grouping was enhanced.

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